Gas-liquid, gas-slurry, and gas-sludge reactions (hereinafter referred to collectively as gas-liquid reactions) present unique problems not found in single phase reactions. The rate and efficiency of gas-liquid reactions is dependent on the amount of contact between the gas and the liquid. The contact occurs at the interface of the liquid and the gas and is, therefore, dependent upon the surface area of the gas bubbles in the liquid. For a given amount of gas, the smaller the bubbles, the greater the surface area. It is therefore advantageous to produce smaller bubbles in order to achieve the best reaction efficiency.
The efficiency of gas-liquid reactions is particularly important in wastewater treatment systems. For example, one of the primary processes in treating municipal and some industrial wastewater streams is known as an activated sludge system. In an activated sludge system, incoming wastewater, typically under gravity flow conditions, enters a large, typically rectangular aeration basin. Within the basin a manifold system of aerators served by one or more large air compressors puts air into the wastewater. The oxygen in the air allows naturally occurring bacteria (the activated sludge) to oxidize contaminants in the wastewater.
The aerators used in conventional wastewater treatment plants are typically disks with small pores which are referred to as diffusers. Conventional diffusers are able to produce bubbles in the 100-500 micron range. These relatively large bubbles tend to rise quickly in the aeration basin, limiting the amount of oxygen that can transfer from the gas bubble to the water. As a result, extremely large quantities of air must be passed through the diffuser in order to ensure that an appropriate amount of oxygen enter the water.
Conventional diffusers tend to plug over time. When a diffuser is plugged, the air pressure behind the diffuser can blow the diffuser head completely off of the riser pipe to which it was attached. If a diffuser head blows off of the riser pipe, the pressure drop across the diffuser is eliminated. As the diffusers and riser pipes are manifolded together, any reduction in pressure drop reduces efficiency across the entire system.
Replacing a conventional diffuser requires that the activated sludge system or a portion of the system be taken off line and drained so that the diffuser may be replaced. Thus, a need exists for improvements in the art of diffuser design which facilitate the generation of sub-micron sized bubbles in the wastewater treatment systems.
Diffuser manufacturers have heretofore attempted to generate sub-micron sized bubbles in activated sludge systems by fabricating diffusers with very small outlet holes. All such attempts have been unsuccessful because the problem of diffuser plugging is exacerbated when diffuser outlet hole size is reduced.